In coronary artery disease, the coronary arteries become narrow or blocked due to a gradual build-up of atherosclerotic plaque that affixes to the inner surface of the arterial wall. These lesions restrict the flow of blood through the diseased artery, and, if left untreated can result in complications that include acute myocardial infarction. The first percutaneous transluminal coronary angioplasty (PTCA) was performed in 1977, and has become a common medical intervention to revascularize diseased arteries. In a typical PTCA procedure, a small dilatation balloon is positioned across a targeted lesion and inflated to increase the luminal diameter of the affected artery. Most of the improvement in luminal diameter following balloon angioplasty results from the stretching of the arterial wall by the balloon, however plaque compression, splitting and axially redistribution can also contribute to an increase in luminal diameter.
In a typical PTCA procedure, the diseased coronary artery is accessed from a peripheral artery such as the femoral and brachial arteries. From the peripheral artery, the distal end of the catheter must navigate through the curves and bends of a tortuous vascular tree to reach a targeted lesion in an affected artery. Typically, a guidewire is used to establish a mechanical pathway to the site of the lesion, allowing the catheter to track the guidewire from the peripheral artery to the targeted lesion. To successfully track the guidewire through the tortuous vasculature, a catheter having a relatively flexible distal portion is required. On the other hand, a rather stiff proximal portion is generally prescribed to provide the pushability needed to advance the catheter along the guidewire.
A traditional limitation of PTCA is the treatment of totally occluded arteries. As indicated above, the PTCA protocol requires the positioning of a dilatation balloon across the lesion and thus a passageway through the lesion is required. Conventional catheters designed with flexible distal portions for trackability lack the necessary stiffness to advance through an occluding lesion, and thus have been generally limited to the treatment of partially blocked arteries.